Vaults

The higher reaches of the Underdark consist of immense networks of relatively small caves, but as a traveler descends, the number of caves decreases as the size of the individual caves increases. A large cave near the surface may consist of a few dozen linked chambers, each perhaps a few hundred feet long and a few dozen feet wide. But deeper down are openings in the earth that dwarf any surface dweller’s conception of a cave.

A typical vault may be 2 to 4 miles across and as much as 1 mile high. Some, however, sprawl for 50 miles or more and reach heights of 5 or 6 miles from the floor. Larger vaults often feature immense columns-huge piers of natural rock that help to buttress the soaring ceiling. Some were formed by unthinkably massive pieces of the world grinding past each other in the very dawn of time, and yet others by the influence of the Underdark’s native magic. However it was formed, a vault is a world in miniature, with its own streams, lakes, hills, and plateaus all contained in a single vast cavern.

Vaults are almost always highly desirable territories, since they usually offer enough space and resources to support huge forests of fungus, moss, and other strange growths. By Underdark standards, most vaults teem with life, so it comes as no surprise that they support the most powerful and numerous of Underdark settlements. Some stories even tell of illuminated vaults, places where sun-bright crystals in the ceilings blaze with the intensity of true daylight and support green plants and surface like fauna in abundance.